I'm planing on backpacking across Europe next year and I hate being the dipshit who only speaks one langue. I already have a small amount of german and spanish so those are the only two I'm interested in. I get the impression that outside of Spain spanish isn't spoken much but I do plan on traveling south america at some point too so spanish is going to be needed eventually.
People will almost certainly prefer speaking English to you outside Spain or the German-speaking countries, and also probably inside them, sadly. Just learn a couple of useful words per country as you travel, some places love that shit. Sounds like you are a little more motivated to learn Spanish, which counts for a lot, so I would go with that.